The microcirculation and correlated histology of healing bone, under different conditions of repair, are being investigated against the background of normal circulation in laboratory animals. Microangiography is the chief investigative tool in survival experiments of different durations, mainly on dogs. Standard histologic, tetracycline fluorophore, and blood flow observations are included. The results of fracture, internal fixation, bone grafting, implantation of foreign materials, and thermal necrosis of bone are being examined. Experiments on the normal blood supply of major canine joints, and on the microvascular and correlated histologic effects of joint degeneration and injury, will be added to the studies. The broad objectives of the project are to describe and document the vascular and histologic details of the reparative processes of animal bone as similar to human bone as possible, and to show clinical applications.